1. Field of the Invention
The present invention relates to novel aqueous dispersions of an alkenyloxysilane-based silicone, which novel dispersions are crosslinkable into elastomeric state by elimination of water therefrom.
2. Description of the Prior Art
U.S. Pat. No. 2,891,920 describes a process for emulsion polymerization of polydiorganosiloxanes utilizing an acidic or basic catalyst in the presence of anionic, cationic or nonionic surface-active agents. The '920 patent relates that the emulsions obtained are stable in storage and, after addition of fillers, can be used to formulate paints for providing continuous coatings by elimination of water therefrom.
U.S. Pat. No. 3,294,725 describes, in particular, the use of dodecylbenzenesulfonic acid to polymerize polydiorganosiloxanes in emulsion. This '725 patent observes that to obtain stable emulsions it is desirable to adjust the pH of such emulsions to a value of approximately 7. It also relates that an elastomeric coating can be obtained from these neutralized emulsions, to which colloidal silica and a polyalkoxysilane have been added.
U.S. Pat. No. 3,360,491 is similar to the '725 patent, except that dodecylbenzenesulfonic acid is replaced with lauryl hydrogen sulfate.
U.S. Pat. No. 3,697,469 describes a particular process for emulsion polymerization of polydiorganosiloxanes and indicates the possibility of adding colloidal silica and a tin salt to the emulsion in order to provide an elastomeric coating by water evaporation.
French Patent FR-A-2,110,358 describes a silicone emulsion having a pH of between 6.5 and 9, crosslinking to an electrically conductive elastomer after evaporation of water and incorporating carbon black. The emulsion, additionally containing a tin salt and a polyalkoxysilane, is not stable in storage and must be stored in two separate packages (two-component emulsion).
U.S. Pat. Nos. 4,221,688 and 4,244,849 and French Patent FR-A-2,463,163 describe storage-stable silicone emulsions comprising:
(i) an anionically stabilized emulsion of an .alpha.,.omega.-(dihydroxy)polydiorganosiloxane; PA1 (ii) a siliceous filler; PA1 (iii) a tin salt; and PA1 (iv) optionally, a nonreinforcing filler. PA1 (A) 100 parts by weight of an oil-in-water type emulsion of an .alpha.,.omega.-(dihydroxy)polydiorganosiloxane, stabilized with at least one surface-active agent selected from among anionic and nonionic surface-active agents and mixtures thereof; PA1 (B) 0.1 to 20 parts by weight of an alkenyloxysilane of the formula: ##STR1## in which R.sub.1, R.sub.2 and R.sub.3, which may be identical or different, are each a monovalent hydrocarbon radical containing from 1 to 12 carbon atoms, with the proviso that R.sub.2 may be a hydrogen atom; PA1 (C) 0.01 to 3 parts by weight of a metal curing catalyst compound; and PA1 (D) 0 to 250 parts by weight of a nonsiliceous inorganic filler material;
The siliceous filler may be a colloidal silica (U.S. Pat. No. 4,221,688), sodium silicate (U.S. Pat. No. 4,244,849) or an amorphous silica powder (FR-A-2,463,163).
In comparison with the known aqueous emulsions (dispersions) of the prior art, these three patents offer, on the one hand, that to obtain a storage-stable single-component emulsion, the emulsion must be stored at an alkaline pH higher than 8.5 or 9, preferably higher than 10 and, on the other hand, a tin salt must be incorporated in the emulsion to shorten to a few days the emulsion ripening or aging stage required to provide a crosslinkable dispersion.
U.S. Pat. No. 3,355,406 describes a silicone latex of an .alpha.,.omega.-(dihydroxy)polydiorganosiloxane, preferably prepared by emulsion polymerization, and of a sesquisiloxane resin including RSiO.sub.1.5 recurring units (R=hydrocarbon residue). The latex may additionally comprise a metal curing catalyst and an alkyltrialkoxysilane.
In U.S. Pat. No. 4,554,187 the silicone resin used in combination with the .alpha.,.omega.-(dihydroxy)polydiorganosiloxane is a reactive resin of low molecular weight, containing alkoxy or acyloxy groups.
In Patent Application EP-A-266,729 the silicone resin used in combination with the .alpha.,.omega.-(dihydroxy)polydiorganosiloxane and with the curing catalyst is a siliconate.
A silicone resin comprising up to 10% by weight of hydroxyl groups may be used in combination with this siliconate.
U.S. Pat. No. 4,618,642 describes an aqueous dispersion of a silicone comprising a nonsiliceous filler and an alkoxysilane or a ketiminoxysilane. According to U.S. Pat. No. 4,608,412, an alkyl orthosilicate can also be employed.
The use of an alkoxysilane in combination with a siliceous filler is described, furthermore, by U.S. Pat. No. 4,618,645.
Alkenyloxysilanes are known compounds, described in particular by FR-A-1,439,013, the combined use of which with an .alpha.,.omega.-(dihydroxy)diorganopolysiloxane and a curing catalyst, in the absence of atmospheric moisture, provides a single-component composition which is stable in storage in the absence of water and which crosslinks into an elastomer in the presence of atmospheric moisture, as per U.S. Pat. No. 3,819,563.
However, U.S. Pat. No. 3,819,563 neither describes nor suggests that the silicone composition may be in the form of an aqueous dispersion.
Furthermore, the literature pertaining to aqueous silicone dispersions does not describe the use of alkenyloxysilane in combination with an aqueous emulsion of an .alpha.,.omega.-(dihydroxy)diorganopolysiloxane and a metal curing catalyst.